Specifically, the hippocampus—-a brain region associated with learning and memory--was twice as large.

In addition, the brain cells of the aerobic mouse could sustain
longer bouts of "long-term potentiation," the increased efficiency of
communication between neurons that occurs after neurons fire.

Better learning, too

Did these changes translate into better learning? Indeed they did.
Mice who exercised performed better on a spatial learning task (finding
their way through a water maze).

Why does it work?

Exercise is known to improve mood. Might that explain these results? Perhaps animals learn better when they feel better.

The explanation sounds plausible and may account for some of the effect. But it seems pretty clear there is more going on.

Since the late 1990s, research has revealed that aerobic exercise

boosts levels of brain-derived neurotrophic factor (BDNF), a substance essential for the growth of brain cells

stimulates neurogenesis—the birth of new neurons

mobilizes the expression of genes that are believed to enhance
brain plasticity—i.e., the ability of the brain to change its neural
pathway, and

prevents brain tissue loss in older adults

(For reviews, see Cotman and Berchtold 2002 and von Pragg 2008).

What about exercise for children?

Much of what we know about the cognitive effects of exercise comes from brain research
on rodents, not humans. But some studies have been conducted on kids, and the results
suggest that aerobic exercise can make children more focused and less
impulsive.

For example, school children
were asked to view some images of animals and make quick judgments
about them ("Is it a cat or a dog?"), physically fit kids had faster reaction times, and their brains showed evidence of more
extensive processing during the task (Hillman et al 2005). Other brain research suggests that fit kids are better at filtering out task-irrelevant information (Kamijo et al 2015).

Studies also indicate that fit children tend to have greater brain volume in the hippocampus, a brain region associated with memory (Chaddock-Heyman et al 2014), and these kids show signs of enhanced long-term retention. In one study, kids memorized new places on a map equally well, regardless of their fitness levels. But when they were tested on their retention the following day, the higher fitness children performed better (Raine et al 2013).

Intriguing? Yes. But these studies report correlations only. They can't prove causation. What if more focused, quick-thinking kids are more likely to seek out physical activity? That could explain the results. We need randomized, controlled experiments (Janssen et al 2014). And in recent years, there have been several.

Mounting evidence: What experiments reveal about the cognitive benefits of exercise for children

Exercise and attention

Does a quick bout of exercise make kids more attentive?

In one recent experiment, kids who ordinarily
performed poorly on attention tasks improved their accuracy when tested
shortly after "moderate acute exercise" -- 20 minutes of walking on a
treadmill (Drollette et al 2014).

Another experiment randomly assigned 56 school kids to one of three morning school sessions:

sitting all morning

getting a
20-minute break of physical activity after 90 minutes; and

getting two 20-minute physical
activity bouts, one at the start and after 90min

The kids
who got two bouts of morning exercise performed better on a test of
attention, and this was true even after the researchers adjusted for
baseline differences in attention and children's involvement in sports
(Altenburg 2015).

And what
about ADHD? When researchers tested the effects of short-term exercise
on kids diagnosed with ADHD, they found that aerobic activity gave these
kids a special boost, altering their brain activity in ways that might
enhance self-discipline (Pontifex et al 2013).

These studies
address immediate, short-term responses to exercise, and lend support
the idea that school recess periods -- breaks for play and physical activity --
can enhance attention in the classroom. But there are also studies that
address long-term benefits of exercise for children.

For instance, what
happens if you enroll previously sedentary kids in a program of
daily physical exercise? One randomized, controlled study of overweight children found that 40 minutes a day of aerobic exercise improved executive
function, that aspect of intelligence that helps us pay attention, plan,
and resist distractions (Davis et al 2007).

Another experiment replicated these results,
and found that 13 weeks of aerobic exercise was also linked with
improved math skills and increased activity in the bilateral prefrontal
cortex, a brain region associated with executive function (Davis et al
2011).

Similarly, when Keita Kamijo and colleagues randomly assigned 20
youngsters (aged 7-9 years) to an after-school exercise program, kids
who got 70 minutes of moderate to vigorous physical activity each day
showed improvements solving tasks that taxed executive control and
working memory (Kamijo et al 2012). Kids in a control group did not.

And
a recent randomized study of more than 220 school children found that
kids assigned to engage in 60 minutes of daily, after-school aerobic
activities performed better on tests of focus and cognitive
flexibility--the ability to switch between tasks while maintaining speed
and accuracy (Hillman et al 2014).

So we've got evidence that exercise can improve a child's ability to focus.
But does that translate into better academic performance? There is
reason to think so.

Physical exercise and academic achievement

Studies suggest that physical exercise yields short- and long-term benefits on achievement in the classroom.

For instance, one experiment found that a 20
minute session of walking boosted children's subsequent performance on tests of
reading, spelling, and arithmetic (Hillman et al 2009a). Another study found that kids who exercised 10-20 minutes prior to a math test outperformed kids in sedentary control group (Howie et al 2015).

And the long-term? As noted above, one randomized study found that kids showed improved mathematics
skills after a 13-week exercise program (Davis et al 2011), and other research indicates similar benefits.

In an experiment performed by Daniel Ardoy and colleagues on 67 adolescents, some kids were assigned to get 4 sessions each week of high intensity PE. After four
months, these kids performed better than other kids on tests of cognitive
ability and earned higher grades at school (Ardoy et al 2014). Adolescents assigned to less intense PE workouts showed no showed no cognitive improvements
over kids in the control group (Ardoy et al 2014).

More recently, kids who were assigned a daily schedule with more physical activity breaks outperformed their control-group peers in mathematics and reading (Tomporowski 2016).

Exercise for children:

A safe bet...but make it fun

Can we assume that exercise will help every child perform better in school? Perhaps not. In some studies of aerobic
exercise, the reported effects have been small or non-existent. As
Caitlin Lees and Jessica Hopkins (2013) argue, we need more rigorous
research to better understand what's going on. We need to learn more about the details -- including how the effects
vary by intensity, frequency, and type of exercise being performed.

But the results aren't "mixed" in the sense that we don't know if exercise is good or bad for the brain. Clearly, it's good for the brain. Nor are the results "mixed" in the sense that we don't know if exercise during the school day helps or hurts academics.

When researchers conducted a meta-analysis of 59 studies published over the previous 60 years, they found that physical activity has a decidedly positive effect on children's achievement and cognitive outcomes (Fedewa and Ahn 2011).

There is no evidence that it's detrimental, which is striking if you consider that time spent by children in recess and physical education class is time diverted from academic study.

When schools have allocated more time for physical activity, they tend to see cognitive improvements. The worst case scenario is that kids become more fit and healthy, while their academic achievement levels remain the same (Keely and Fox 2009).

So school policies aimed cutting recess or PE -- in order to make more time for academics -- are misguided. We've got nothing to lose by encouraging kids to exercise, and much to gain. But there’s a catch: Exercise should be fun.

The mouse experiments are based on voluntary wheel-running. When rodents are forced to exercise, they don’t always reap the benefits.

Thus, it's important to find fun forms of aerobic exercise for children. Structured activities--like team sports or dance lessons--are good options. But so are nature walks, tree-climbing,
roller-skating, and playing hide-and-seek.